Anyone have experience with a rotax 277 / Bing 36 carb?

  • Wednesday, March 12, 2014 9:15 AM
    Message # 1516036
    Anonymous
    This is actually on a SCAT hovercraft and I have had a real pain trying to get it to run properly. It is really bizarre because there is just nothing to these things. Since these were very popular in ultralights I was thinking maybe some of the members here have experience with them. The engine and carb were rebuilt with all new jets and wear parts. 

    If anyone has or knows of someone that has a running 277 locally it would be awesome to try and swap a carb off a running motor on there and verify that as the only issue. Thanks
  • Thursday, March 13, 2014 8:55 AM
    Reply # 1516815 on 1516036

    Matt,

    You didn’t mention what symptoms the engine is experiencing. The Scat Hovercraft Company were having running issues after a few engine/carb rebuilds. It was found either the fuel pump was at fault or air leakage in the engine case. Below are a couple sites that may help.


    https://groups.yahoo.com/neo/groups/rotax/conversations/topics/183

    http://www.rotaxowner.com/rotax-forum/4-general-discussion/4428-rotax-277-time-to-call-in-the-tropes

  • Friday, March 14, 2014 3:48 PM
    Reply # 1517854 on 1516036
    Anonymous
    Thanks for the link but it does not appear to be working. It will not load. 

    I kind of intentionally didn't list the symptom because I didn't want to write an overly long intimidating thread if no one had any experience anyways. Here is my most pressing issue and I know this sounds unbelievable simple but believe me I have spent way to much time messing with it. I cannot get the fuel bowl needle to seat properly. I have a new needle as well as the one that was in there and I have played around with every position of the floats you can bend them to. As a result the thing wants to overfill with fuel which in theory is making it run really rich. now that I write that it seems really simple but I have a feeling their are other things going on because every now and then I have had brief periods where it would seat properly but it still was running really rough, not wanting to idle and not getting full power.

    What makes me think it isn't necessarily just this is that The only way to get it to start is to give it a shot of gas mix from a spray bottle and then leave the choke on. It will idle high for maybe 10 sec and then it backfires through the carb and dies. Liking to run with the choke on tells me the carb is running lean not rich. 

    It does have a new fuel pump as well. 
    Last modified: Friday, March 14, 2014 3:51 PM | Anonymous
  • Wednesday, March 19, 2014 8:28 AM
    Reply # 1520710 on 1516036
    Mathew,

    These are two differnt links and worked great this morning, there is talk on each site of similar issues you are having. Hope you get it running..flying season is soon.
  • Thursday, March 20, 2014 8:09 PM
    Reply # 1521933 on 1516036
    Deleted user
    My 2 cents ref float bowl needle seating. Look at the tip of the needed and the seat. Any signs of wear make then un-serviceable. If they are ok then it is likely the angle of the needle to the float - and you may have to seat the needle by giving it a gentle tap or two. Any misalignment with the float plate can make the needle wiggle unreliably. If the needle has a rubber tip, it may not be bonded properly. Magnifying glass time!
    How much head pressure does the new pump make? Try connecting a small gas tank just a few inches above the float and see if that works. 
    From several hrs of terrestrial-bound 2-cycles, one of the odd things I found that made improvements all 'round was to get the best plugs I could find, usually NGK's. 
    If you have primary and secondary compression, gas, air, and a spark - toss it and buy a a pizza!

  • Friday, April 04, 2014 8:01 AM
    Reply # 1531234 on 1516036
    Anonymous
    I've got a new float, needle, and shaft coming in the mail. Being that the float is the only thing I didn't replace I think it just makes sense. 

    My thought is that it is possible that the float is somewhat fuel logged and while it does seem to float it's additional weight and loss of flotation is allowing the needle to pop off under less pressure. This combined with a brand new pump may be causing problems. 

    I find it hard to believe that this is what is causing all of my problems but I need to get this taken care of before trying to chase anything else down. Hopefully it will solve the problem but if not, now I will be able to rule it out. 

    Thanks for the ideas Malcom, and If I still am flooding the bowl with the new float I will try your gas tank idea. 
  • Tuesday, April 08, 2014 9:36 AM
    Reply # 1533753 on 1516036
    Anonymous
    FWIW I think I got these issues resolved and it was kind of an odd one. 

    Saturday I decided to double check the timing. I didn't think the key was sheared but I thought maybe the stator / pick coil plate had been rotated some because the way ran just seemed like the timing was 10° or so off. When I pulled the flywheel, sure enough the key was sheared. Usually with a sheared key it won't run at all because it will be so far off. Fixed that but the bowl was still flooding and it still wouldn't idle well even if the bowl was filled and fuel pump disconnected. (I had put a new NV and float in. 

    I determined that the valve was definitely seating but the pump was giving enough pressure to force the floats into the gas and lift the valve seat which is why it was flooding. This was a stock pump though so the problem had to be in the float mechanism still. Now when I got this project it was a project and the guy had a box of about 10 bing 54's. I had grabbed the cleanest body, bowl and slider, cleaned it more and put all new internals in. So I looked through the other carbs sitting there and I noticed a small stamp most of them were stamped 54/38/xxx  but 2 have a 54/36/xxx stamp. I then noticed that the NV seats on the two with the /36 stamp where 1/3 of the diameter of the others. Obviously this reduction in area will allow the valve to hold far more fuel psi. Since the 277 takes a 36mm carb this also seemed to jive better (even though I don't know what the numbers really are) . I cleaned that one up got it on and it seems to be running much better and it no longer over fills the bowl. 


  • Tuesday, April 08, 2014 1:58 PM
    Reply # 1533968 on 1516036
     
    Well done Mr. Curcio!

    Hats off for sticking with this problem and getting it solved. 

    Hope to see you at the Owner / Operator Maintenance Meeting tonight.
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